Nankai-trough earthquake scenario

2009 Chi-Chi Conference in Taipei
Strong ground motion and Tsunami Simulation for the
Nankai-Trough Mega-thrust Earthquake Using
Supercomputers
Takashi FURUMURA 古村孝志
CIDIR/ERI, The University of Tokyo
東京大学情報学環総合防災情報研究中心/地震研究所
Nankai-Trough Earthquakes
Hokkaido
Honshu
Shikoku
Kyushu
Strong Ground motion from the 1944 Tonankai earthquake
1854 Ansei Edo(M8.4)
安政東海地震
Shizuoka
500 km
Seismic Energy
x 200-500
Old JMA Intensity (max 6)
The earthquake generate firstly
strong ground motions with JMA
intensity of 6-7 occur widely along
the source region of 300- 500 km long.
Coseismic surface deformation due to the earthquake
After 1946 Nankai Earthquake
Kochi
Downtown Kochi高知 City Today
1946 Nankai Earthquake
Subsidence
Photos, Courtesy from Prof. Okamura, Kochi Univ.
Then, just after the earthquake
coseismic surface deformation
upheaves or subsides coastal lines
more than 1-2m along the source zone.
Uplift
Continental Plate
Amplification and long-time prolongation of tsunami
Tide-gouge record at Tosashimizu
土佐清水 during the
1946 Nankai Earthquake
1m
5 hours
Photo:
JMA Tokushima
Finally, tall tsunami more than 15 m attack wide area along the
coast, and it is lasting more than
several hours.
An Integrated Ground Motion,
Coseismic Deformation, and
Tsunami Simulation
Integrated Ground motion and Tsunami Simulation
(1) Ground Motion and
Coseismic Deformation
(2) Tsunami Generation
and Propagation Simulation
3D FDM simulation of Equation of Motion
3D FDM simulation of Navier-Stokes Equation
u  u   u  p   u  g
    2  u      u
u
Input
Seafloor
Deformation
D (x,y,t)
Ground motion (Vertical, Displacement)
Seasurface elevation (Tsunami)
Furumura and Saito (2009) - 1896 Meiji Sanriku Earthquake
Integrated Ground motion and Tsunami Simulation
D=4m, W=20km, h=8000m
(a) Short Rise Time (Ts=10s)
normal event
8000m
slow event
(b) Long Rise Time (Ts=120s)
8000m
Very slow-rupture earthquakes occurring
below deep sea cannot generate tall
tsunami because tsunami propagating
quickly away from the source region
Saito and Furumura (2009)
Integrated Ground motion and Tsunami Simulation
Dispersion of Tsunami propagating in
deep sea cause elongating and complex
tsunami waveform.
Such effect is naturally taking into
accounted in present simulation.
Cape Muroto
2004 Off Kii-Pen.
Earthquake (M7.4)
(a) Navier-Stokes Model
OBS
After JAMSTEC
Tsunami waveform, off Cape Muroto 室戸岬沖
(b) Linear Long Wave Model
Integrated Ground motion and Tsunami Simulation
Tsunami Waveform 3D/1D
(2) Tsunami Simulation
米良
内浦
松坂
土佐清水
(1) Ground motion Simulation
Subsidence
Uplift
(a) 3D Model
Furumura and Saito (2009)
(b) Half-space Model
Source-rupture Scenario for future
Nankai-Trough Earthquake
Nankai-trough mega-thrust earthquake scenario
Question: The Hoei 宝永Earthquake in 1707 was the largest model?
Seismic Intensity
Tsunami Height
Coseismic
Deformation
-2 m
2m
Source Model: An’naka (2003)
Re-evaluation of the 1707 Hoei Earthquake Model
1896 Nankai
1854 Ansei
1707 Hoei
1361 Shohei
684 Hakuho
Recently Tsunami deposits during the
1707 Hoei Earthquake was observed
at Ryujin pond （龍神池） by e.g.
Okamura et al. (2004), indicating
extension of source-rupture area to
west.
Okamura (2008)
龍神池
写真
-2 m
2m
Photo: Courtesy from Prof. Okamura
津波池
Tsunami Pond
Re-evaluation of the 1707 Hoei Earthquake Model
Geological Tracing
Tsunami Deposits
e.g. Okamura (2008)
1707 Hoei Earthquake model
龍神池
Kyushu
Hguga-nada Segment (M7.5)
Back-slip model from GPS data
Nishimura et al. (1999)
Philippine-sea Plate Model
Nakajima and Hasegawa (2007）
日向灘の固着
地震発生帯
（固着域）の深さ
We assume an additional
fault segment at
Huganada based on new
geological and
seismological findings in
order to explain crustal
deformation and tsunami
in eastern Kyushu
Re-evaluation of the 1707 Hoei Earthquake Model
(1) NEW Hoei model Tsunami Simulation
Height of tsunami at the Ryujim Pond from
the new source model is 2 - 4 m which is
twice larger than that for the previous Hoei
source model. Moreover delayed rupture in
the segment of Hguga-nada cause increase
tsunami height over 6 m.
(1) NEW Hoei model with delayed rupture (14min)
Ground motion simulation for new Hoei Source Model
1707 Hoei Model (An’naka, 2003)
Simulated Ground Motion
Miyazaki
1707 Hoei Model
10 cm/s
20 cm/s
50 cm/s
New model
(Hyuga-nada segment)
PGV
NEW Hoei Model (N5: Hyuga-nada)
10 cm/s
20 cm/s
50 cm/s
PGV
Simulation for the Nankai-trough Earthquake
SUMMARY
(1) Integrated simulation of ground motion and tsunami
- We developed an integrated simulation model for evaluating
strong ground motions, coseismic deformations, and tsunami by
combining FDM simulation of 3D equation of motions and 3D
Navier-stokes equations.
-The new simulation model offers direct means for total
understanding of complicated disasters due to the occurrence of
the Nankai-trough earthquake consistently and accurately.
(2) Nankai-trough earthquake scenario
-We revised the source model for the 1707 Hoei earthquake to cover
the rupture area to Hyuga-nada in order to explain coseismic
deformation and tsunami deposits at Tsunami ponds at Kyushu.
-Expected tsunami and strong ground motion in eastern seaboard of
Kyushu is 1.5-2 times larger than that we expected from the previous
model.
Re-evaluation of the 1707 Hoei Earthquake Model
Tsunami propagation from the new Hoei model
Height of tsunami along the
coast of Hyuga-nada using the
new source model is about 2-4
m which is twice larger than
the previous source model.

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